The present invention relates to a cylinder identifying device to identify the cylinder or cylinders of a running internal combustion engine in a specific stroke, and more particularly to a cylinder identifying device for internal combustion engines suitable for automotive use.
A cycle of the operation of an internal combustion engine consists of a plurality of strokes, two or four, and accordingly it is necessary for controlling the timing of ignition, fuel injection or the like of a multi-cylinder combustion engine having two or more cylinders to identify the cylinder or cylinders in a specific stroke, e.g. a compression stroke. This requires a cylinder identifying device.
According to the prior art, there are a number of such cylinder identifying devices. A first embodiment of the prior art for this purpose, as illustrated in FIGS. 2 and 3 of the Japanese Patent Laid-open No. Sho 63-37336, the compression stroke of a first cylinder is identified with signals from a crank angle detecting sensor and a cylinder identifying sensor fitted to the camshaft.
According to a second embodiment of the prior art, as disclosed in the Japanese Patent Laid-open No. Hei 5-86953, three projections for crank angle identification are provided at unequal intervals on a revolution detecting disk mounted on the camshaft; a projection for identifying a first cylinder is added so that a plurality of signals be generated at unequal intervals; the arrayed state of the pulse intervals of this plurality of signals is checked; the crank angle is identified at a point of time when a prescribed array pattern attributable solely to the crank angle identifying pulse is detected; and the cylinder is identified at a point of time when a prescribed array pattern including the cylinder identifying pulse is detected or when a variation in a prescribed pulse interval is detected at a cylinder identifying pulse. The method to identify the cylinder at a point of time when a variation in a prescribed pulse interval is detected is briefly described below with reference to FIG. 2. FIG. 2, referring to a three-cylinder internal combustion engine, illustrates the relationship between the stroke of each cylinder and the position of detection by the crank angle sensor. Marks .largecircle. for strokes denote suction, and arrows indicate positions of ignition. For the compression stroke of each cylinder, two signals (A, B) are generated, and there further is a signal C for the detection of the compression stroke of one cylinder. Two revolutions of the crankshaft in the diagram constitute the basic cycle of a four-stroke internal combustion engine. Detailed positional relationships among the signals A, B and C in FIG. 2 are shown in FIG. 3. A signal CR signifies the generating position of a signal to be detected by the crank angle sensor. The signal A is generated 75.degree. before the top dead point of compression of each cylinder. The signal B is also generated 5.degree. before the top dead point of compression of each cylinder. The signal C is generated only once in two revolutions of the crankshaft in a position 210.degree. before the top dead point of compression of one cylinder, and the angle between signals C is narrower than for other signals. Cylinder identification is finalized when the condition of identification given in the table is met. More specifically, the identification is made according to Formula 1 on the basis of the hysteresis of the time between signals CR. EQU TRATIO.gtoreq.MKRAT# Formula 1
where MKRAT# is a cylinder identification coefficient, and TRATIO is the pulse period ratio.
Calculated is done by Formula 2. EQU (Told1+Told2)/T Formula 2
where Told1 is the pulse period immediately before, Told2, the pulse period immediately before Told1, and T, the latest pulse period.
Said MKRAT# takes a value of 5 or so. Thus, as converted into an angle ratio, at the time of the generation of a signal C, Told2 is 175.degree., Told 1, 65.degree., and T, 35.degree., so that TRATIO=(175+65)/35=7.5. Similarly, at the time of the generation of a signal B, Told2 is 65.degree., Told 1, 175.degree., and T, 65.degree., so that TRATIO=(65+175)/65=3.7. At the time of the generation of a signal A, Told2 is 170.degree., Told 1, 65.degree., and T, 170.degree., so that TRATIO=(175+65)/170=1.38. To sum up, as TRATIO is 1.38 at the time of signal A generation, 3.7 at the time of signal B generation, and 7.5 at the time of signal C generation, the signal C can be discriminated from the signals A and B if the cylinder identification coefficient MKRAT# is set to be 5.
However, first, the first embodiment of the prior art referred to above involves the problem that, when the internal combustion engine is started, no cylinder identification can be done until the camshaft completes a maximum of one full revolution, i.e. until the crankshaft completes two revolutions. Then, the second embodiment of the prior art, though stroke identification of the internal combustion engine is promptly done, there is a risk of misidentification if the internal combustion engine widely fluctuates in revolution because the identification is based on the time ratio among signals. Furthermore, since it has only one sensor for detection of revolutions (crank angle sensor), though it has a cost advantage, it entails the problem that the internal combustion engine will stop in the event of sensor failure.